1. Field of the Invention
The present invention relates generally to an apparatus for loading a printer with a recording medium, and more particularly to an automatic medium loading apparatus which incorporates a mechanism for operating a paper bail between operated and retracted positions.
2. Discussion of the Prior Art
In a printer, or a printing mechanism incorporated in a typewriter for example, a recording medium such as a cut sheet is supported by a suitable support member such as a platen, and a portion of the medium is held in place on the support member by a suitable medium guide member such as a paper bail, which prevents the leading portion of the medium from being lifted away from the support member. The medium support member is supported by a frame of the printer such that the support member extends parallel to a direction of movement of the printing mechanism (including a print head mounted on a carriage or carrier). The medium guide member has presser members and is pivotally supported by the printer frame such that the presser members are moved between a first or urging position for urging the recording medium against the medium support member, and a second or retracted position in which the presser members are spaced apart from the medium support member. Normally, the medium guide member is maintained in its first position by suitable holding or biasing means.
The recording medium suitably loaded on the printer or printing mechanism is automatically fed or advanced by a suitable distance at the end of printing each line on the medium. The printer incorporates a medium feeding mechanism which includes a medium feeding motor. This mechanism cooperates with the medium support and guide members to constitute a medium feeding and advancing device. This device may have an automatic medium loading function for automatically feeding and advancing the recording medium to a predetermined printing start position prior to starting the printing operation on the medium. When this automatic medium loading operation is accomplished, it is necessary to move the medium guide member to its second position, so that the leading end portion of the automatically advanced medium may pass between the medium support member and the medium guide member. In view of this requirement, a medium feeding and advancing device is proposed in laid-open Publication No. 61-197263 (published in 1986) of unexamined Japanese Patent Application No. 60-39462, wherein the medium feeding motor is utilized as a drive source for operating the medium guide member to its second position, upon automatic loading of the recording medium.
The feeding and advancing device disclosed in the above-identified publication includes: a release member which is driven by the medium feeding motor, to operate the medium guide member to the second position; a clutch which is operable between an operated position for transmitting the drive force of the motor to the release member and a non-operated position in which the motor drive force is not transmitted to the release member; and a clutch regulator for controlling the clutch in relation to the movement of the printing mechanism. The clutch regulator includes a switching device for normally holding the clutch in the non-operated position, and for switching the clutch to its operated position when the printing mechanism is moved to a predetermined medium loading standby position. The clutch regulator further includes a control device adapted to move the printing mechanism to the medium loading standby position, and then moving the printing mechanism to a suitable position such as a printing start position.
When the medium feeding motor is operated after the clutch is switched to the operated position with the printing mechanism moved to the medium loading standby position, the recording medium is fed by feed rollers, and at the same time the medium guide member is operated to the second position by the release member, whereby the presser rollers of the medium guide member are lifted to permit the passage of the recording medium between the medium support member and the presser rollers. When the printing mechanism is moved away from the medium loading standby position, the switching device is returned to a position for holding the clutch in the non-operated position. However, the clutch per se cannot be returned to the non-operated position until the release member is rotated by the medium feeding motor by a predetermined angle to enable the medium guide member to return to its first position.
In the medium feeding and advancing device described above, the movement of the printing mechanism to the medium loading standby position necessarily activates the clutch to its operated position. For the clutch to return to the non-operated position, the medium feeding motor should be operated by an amount necessary to load the printer with the recording medium. Therefore, the medium loading standby position should be located outside the printing area in which the printing mechanism is movable, in order to prevent the clutch from being moved to the operated position, except when the medium loading operation is effected. This means a relatively narrow printing area or a relatively large lateral size of the printer.
Even in the event that the printing mechanism is moved to the medium loading standby position by error, the medium feeding motor should be activated to effect a medium loading operation. This is troublesome, and unnecessarily advances the recording medium if it is already set on the printer. The unnecessarily advanced recording medium should be returned to the original position so that the printing is started at the intended position. This is also troublesome.
Some printers are adapted such that upon power application, the printing mechanism is once moved to a zeroing position beyond the printing area, to establish the zero point of the printing mechanism, so that the printing mechanism is moved to the commanded positions for a printing operation. The printing mechanism may also be zeroed after the top cover of the printer is opened and closed during a printing job, for replacing a ribbon cassette, for example. In such cases, the zeroing position should be spaced apart from the medium loading standby position in the direction toward the printing area, so as to prevent the clutch from being switched to the operated position when the printing mechanism is moved to the zeroing position. Thus, the printing mechanism should be moved to the two different positions for the zeroing operation and the medium loading operation. In a printer disclosed in U. S. Pat. No. 4,264,220, for example, the carriage is zeroed by activating a carriage feeding motor to move the carriage to a predetermined carriage zeroing position and further activating the motor in an out-of-synchronization manner without a displacement thereof, with the carriage held at the zeroing poisition by a suitable stop. In this type of printer, the carriage zeroing position is located at an extreme left or right position of the carriage travel, while the medium loading standby position is located at the other extreme position opposite to the carriage zeroing position. This means increased complexity of the control system for controlling the carriage movements for the carriage zeroing operation and the medium loading operation.
In the case where the carriage zeroing is effected solely based on a signal generated by a detector switch for detecting the zero point of the carriage, the switch should be positioned with extremely high accuracy, in order to precisely position the carriage at its zero point.